As an image display device substitutable for liquid crystal display (LCD), image display devices with the use of technology such as an electrophoresis method, an electro-chromic method, a thermal method, dichroic-particles-rotary method are proposed.
As for these image display devices, it is conceivable as inexpensive visual display device of the next generation from a merit having wide field of vision close to normal printed matter, having smaller consumption with LCD, or having a memory function, and spreading out to a display for portable device and an electronic paper is expected. Recently, electrophoresis method is proposed that microencapsulate dispersion liquid made up with dispersion particles and coloration solution and dispose the liquid between faced substrates.
However, in the electrophoresis method, there is a problem that a response rate is slow by the reason of viscosity resistance because the particles migrate among the electrophoresis solution. Further, there is a problem of lacking imaging repetition stability, because particles with high specific gravity of titanium oxide is scattered within solution of low specific gravity, it is easy to subside, difficult to maintain a stability of dispersion state. Even in the case of microencapsulating, cell size is diminished to a microcapsule level in order to make it hard to appear, however, an essential problem was not overcome at all.
Besides the electrophoresis method using behavior in the solution, recently, a method wherein electro-conductive particles and a charge transport layer are installed in a part of the substrate without using solution is proposed. [The Imaging Society of Japan “Japan Hardcopy '99” (Jul. 21-23, 1999) Transaction Pages 249-252] However, the structure becomes complicated because the charge transport layer and further a charge generation layer are to be arranged. In addition, it is difficult to constantly dissipate charges from the electro-conductive particles, and thus there is a drawback on the lack of stability.
As one method for overcoming the various problems mentioned above, an image display device comprising an image display panel is known, in which image display media are sealed in cells formed in an isolated manner from one another by partition walls between a front substrate and a rear substrate, at least one of two substrates being transparent, and, in which the image display media, to which an electrostatic field is applied, are made to move so as to display an image by means of Coulomb's force and so on.
Further, in the image display panel installed in the known image display device mentioned above, a plurality of cells formed by the partition walls correspond normally one for one to the positions of pixels for displaying the image. However, in the case that the cells correspond one for one to the pixel positions, if use is made of the substrates having bad dimension accuracy (which is especially found in resin substrate), there is a drawback such that the cells and the pixel positions become out of alignment when upper and lower substrates are laminated. Moreover, in the case of aiming for a high definition image display panel, a rate of partition wall cross section occupied on a display surface of the panel becomes higher, and thus there is a drawback such that an opening rate is lowered. Further, if the cell is larger than the pixel, there occurs a movement of the image display media in the cell, and thus there is a drawback such that a display quality if lowered. (Tasks of the first invention)
Moreover, among the techniques mentioned above, in the case of making a color of the overall partition wall equal to a color of one of the image display media, especially in the case of making the overall partition wall to a deep color such as black, if a pigment or a dye having deep color such as black is blended in a resist, there is a drawback such that a light transmission of the resist used for forming the partition wall becomes worse. If a light transmission of the resin becomes worse in this manner, when a light exposure is performed through a mask for a portion to be hardened so as to form the partition wall, a light is not evenly exposed to such portion. Especially, in the case of forming the partition wall having a large height, there is a drawback such that a possibility of generating a developing defect, in which the partition walls are not formed according to a predetermined pattern, becomes higher. (Tasks of the second invention)
The image display device having the construction mentioned above is promising since it is a dry type and has a rapid response speed and a simple construction. In addition, there are high requirements such that: a manufacturing is simple; a connection reliability between the substrate and the partition wall is made higher; and a high opening rate is achieved by making a display area larger. (Tasks of the third invention)